Trigger hold circuit for welding power supply

Abstract

A control circuit for an electric arc welder is responsive to the operation of a torch or gun mounted control switch. A first comparator has one input connected to the gun switch and the other input to a reference voltage source. When the gun switch is closed, the output of the comparator will cause a control relay to be energized. When a welding arc is established, a reed switch closes and provides an input to a second comparator which effectively provides a latch to hold the control relay energized. After a predetermined time delay, typically in the order of 1 second, a timer circuit will provide an output to one input of a third comparator, the other input of which is connected to the gun switch. A subsequent closure of the gun switch will caused the output of the third comparator to change the level of the reference voltage, changing the outputs of the first two comparators, thereby removing the latch and deenergizing the control relay. Thus, the control relay can be deenergized either by the welder operating the control switch a second time or by extinguishing the arc, such as by removing the torch from the workpiece; either will disable the latch circuit and terminate the welding operation.

What is claimed is: 
     
       1. A control circuit for an arc welder including a welding power source, a torch mounted control switch, and means for monitoring the flow of welding current, the control circuit comprising: circuit means responsive to the closure of said control switch for energizing the welding power source, said circuit means including a first comparator having one input connected to said control switch and the other input connected to a reference voltage source;   means responsive to said monitoring means for providing a latch, allowing the control switch to be released without deenergizing the welding power source after sensing the establishment of welding current, said means including a second comparator having one input connected to said current monitoring means and the other input connected to said reference voltage source;   timer means responsive to said monitoring means for providing an output after a first predetermined time delay following the establishment of welding current;   further circuit means responsive to the output of said timer means and to the subsequent closure of the control switch for deenergizing the welding power source, said further circuit means including a comparator circuit having one input connected to said control switch and the other input connected to the output of said timer means whereby said comparator circuit will provide an output upon the closure of said control switch after said predetermined time delay, the output of said further circuit means being connected to modify the voltage level of said reference voltage source thereby to disable said first and second comparators upon the subsequent closure of said control switch; and   means responsive to said monitoring means for deenergizing the welding power source upon sensing the loss of welding current.